- (idiomatic) To use every means possible to achieve a goal, especially in disregarding the harm caused.
- He was more than willing to extend the terms of the loan, but his boss decided to play hardball and demanded a balloon payment.
- (idiomatic) To act rough and ruthless, especially in politics or business.
- So you wanna play hardball?
From the American sport of baseball; the hardball is the heavier and harder type of the two types of throwing ball used when playing that sport.